In the majority of patients with dilated cardiomyopathy the etiology is unknown. Many patients with dilated cardiomyopathy complain of anginal-type pain despite angiographically normal coronary arteries. To examine whether abnormalities in coronary flow exist in dilated cardiomyopathy, arteries, 20 patients with dilated cardiomyopathy and normal epicardial coronary arteries, 8 of whom had frequent chest pain, underwent measurement of great cardiac vein flow and myocardial metabolism at rest and during pacing to a heart rate of 150. After administration of ergonovine, all 8 patients with the history of chest pain experienced their typical chest pain. Compared to patients without chest pain, their coronary flow was lower and coronary resistance higher with significant widening of the AV02 difference suggestive of myocardial ischemia. Additionally, the increase in left ventricular filling pressures was higher in this group. There was no significant change in EKG or epicardial coronary liminal diameter by angiography. Administration of dipyridamole 0.5 to 0.75 mg intravenously to a subgroup of these patients suggested impairment in transmural coronary flow reserve compared to patients without chest pain after ergonovine administration. Thus, patients with dilated cardiomyopathy and chest pain by history may have limited coronary vasodilatory reserve, especially after vasoconstrictor stimulus. Whether this contributes to myocardial damage and dilated cardiomyopathy or is an epiphenomenon of an unrelated etiology, remains to be determined.